Method of making a coulometric device



Dec. 27, 1966 v c. c. BEUSMAN 3,293,731

' METHOD OF MAKING A COULOMETRIC DEVICE Original Filed June 4, 1962 FIG.2

III/[III],

INVENTOR UTILIZATION CURTIS c. BEUSMAN DEVICE FIG. 5 M ATTORNEYS UnitedStates Patent 3 293,731 METHOD OF MAKING A COULQMETRIC DEVICE Curtis C.Beusman, happaqua, N.Y., assignor to purtrs Instruments, Inc, MountKisco, N.Y., a corporation of New York Original application June 4,1962, Ser. No. 199,795, now Patent No. 3,193,763, dated July 6, 1%5.Divided and this application Feb. 10, 1965, Ser. No. 438,456 Claims.(Cl. 29-1555) This is a division of application Serial No. 199,795,filed June 4, 1962, now Patent No. 3,193,763, issued July 6, 1965.

This invention relates to coulometric devices and more particularly to anovel configuration of the components of such devices and to a novelmethod of making such devices.

According to my invention, I provide a body of nonconductive materialwhich has a channel formed therein. A slug of non-conductive materialwhich is free to move along said channel is located in the channel at aposition intermediate the ends thereof. Columns of liquid metal fill thestraight portions of the channel on each side of the slug ofnon-conductive material. A body comp-rising electrolyte material isconnected to each of the liquid metal columns. Means are provided forconnecting an external source of potential across the columns.

A coulometric device according to my invention is especially useful as acurrent integrator and as an operating time indicator, both of theseapplications being known for devices of this general kind.

Moreover, by combining with the basic device any of several means fordetecting the interface between one of the columns of liquid metal andthe slug of nonconductive material, the device may also be made to serveas an electric control device or switch. But the device is especiallyuseful in that it may be made by simple and inexpensive methods, one ofwhich is an integral part of the present invention. My new coulometermay also be made very small and in a wide variety of configurations,sizes and current measuring and time indicating capacities. It has goodresistance to shock and will operate continuously and Well even thoughsubjected to continuing vibration. These and other features will be moreapparent from the description of a preferred embodiment of the inventionwhich will be given below.

The method according to my invention is especially well suited to themanufacture of my new coulometer. It may, however, be used tomanufacture coulometers of other types as well. In my new method Iposition a filamentary body in a predetermined configuration on asurface. I then superpose on said body a layer of nonconductive materialwhich is deformable under pressure and which will retain a permanent setupon release of deforming pressure. Pressure is applied to thesuperposed layer to cause said filamentary body to be impressed intosaid deformable material to form therein a channel having theconfiguration of the filamentary body. The deformable layer is caused toadhere to a base layer of non-conductive material after which I withdrawthe filamentary body from the channel. Liquid metal, the electrodematerial of the coulometer, is then inserted into the channel.

A complete description of a particular coulometer according to myinvention is set forth in the following specification together with afull description of the novel method by which the device may be made. Inthe course of the description reference is made to the accompanyingdrawing in which:

FIG. 1 is an enlarged plan view, partly broken away, of a coulometricdevice according to my invention;

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FIG. 2 is an exploded sectional view, taken along the line 2-2, of thecoulometric device shown in FIG. 1;

FIG. 3 is a sectional view, taken along the line 3-3, of the coulometricdevice shown in FIG. 1;

FIG. 4 is a schematic circuit diagram illustrating one means of usingthe coulometric device of FIG. 1 as an electric switch; and

FIG. 5 is a schematic circuit diagram showing another means of using thecoulometric device of FIG. 1 as an electric circuit controlling means.

Referring now to FIG. 1, a coulometric device according to my inventionconsists of a body of non-conductive material 1. In the particularembodiment of the device here used to illustrate the invention, the bodyof nonconductive material is a flat rectangular plate of transparentmaterial such as vinyl resin or glass. A substantially U-shaped channel2 is formed in the body of the transparent material with the ends of thestraight portions or legs 3 and 4 of the channel adjacent one edge ofthe plate 1. The legs of the channel are connected together at theirother ends by the bow of the channel which is shown at 5. A body ofporous substance such as filter paper 6 which is impregnated with asuitable electrolyte is cast or otherwise formed in the transparentplate such that the electrolyte bearing material extends between the twolegs of the U-shaped channel with portions of the surface of the poroussubstance lying in the surface of at least a portion of the periphery ofeach of the legs of the channel. Two columns of liquid metal fill thelegs 3 and 4 of the channel and extend partially into the bow 5 of thechannel. The adjacent ends of the two columns of liquid metal in the howare separated by any convenient distance by a slug of non-conductivematerial 7 which is free to move along the channel. The slug ofnon-conductive material may be a gas, such as air, or a fluid or even asolid.

Means are provided at the distal ends of the channel for connecting thetwo columns of liquid metal to an external source of potential. In thisparticular embodiment this is accomplished merely by passing conductiveelectrodes, for example, small wires 8 and 9, through the wall of thenon-conductive plate and into the ends of the channel so that they arein contact with the liquid metal in the channel.

In this particular embodiment, the liquid metal forming the two columnsin the legs 3 and 4 of the channel is mercury. The slug ofnon-conductive material 7 between the innermost ends of the two columnsof mercury is a small bubble of air. The electrolyte which saturates theporous substance bridging the columns is a water solution of mercuriciodide. I have found that the solubility of mercuric iodide in water canbe advantageously increased for this purpose by the addition to thesolution of potassium iodide. A satisfactory solution is 0.5 Normal inmercuric iodide and 7 Normal in potassium iodide.

In the particular embodiment here being used to illustrate theinvention, the diameter of the bore of the U- shaped channel is lessthan one millimeter. I have found that channels having a bore up toapproximately three millimeters in diameter are satisfactory where theliquid metal is mercury. Columns of mercury up to three millimeters indiameter possess good capillary characteristics and result in columns ofmercury which are stable in the bore under even extreme conditions ofshock and vibration.

A basic coulometric device such as described above is very useful as anoperating time indicator when connected in an electric circuit by meansof the wires 8 and 9. When a constant direct current potential isimpressed between the leads to the columns of liquid metal, metal ionsare transferred from the anode column through the electrolyte and areplated out on the cathode column with the resutl that the anode columnbecomes shorter and the cathode column becomes longer by the sameamount. This will cause the slug of non-conductive material in the bowof the channel to be pushed by the cathode column in the direction ofthe anode column. If the cross-sectional area of the channel isconstant, then the change in length of the columns is, of course, adirect indication of the quantity of electric charge which has flowed.Furthermore, if the current is also constant, the rate at which metalions are transferred from the anode column to the cathode column isconstant and the displacement of the slug of non-conductive materialthen becomes a direct indication of the length of time the potential hasbeen applied. To facilitate the use of the device as an operating timeindicator, it is convenient to scribe a scale in the face of the body ofthe device along the course of the bow of the channel as indicated at10. It will be apparent to those skilled in the art that the resistanceof the path through which charge flows from the anode column to thecathode column is substantially constant regardless of the relativelengths of the two columns. The accuracy of the device is, therefore,virtually independent of the position of the slug of material which isused as an indicator. Of course, the device will be operative so long asthe slug of non-conductive material does not progress in eitherdirection along the channel beyond the electrolyte material.

A device according to my invention can also be mad to act as anexcellent miniature electric timing switch. One means'of accomplishingthis is to insert a conductive contact through the wall of the body ofthe device and into the channel as indicated for example at 11. Anysuitable external circuit may be connected between the contact 11 andeither of the wires 8 or 9 connected to the columns. So long as thisconductive contact is in contact with the slug of non-conductivematerial in the channel, the external circuit so connected will be open,but as soon as the column of liquid metal which also forms a part of thecircuit grows far enough along the channel so that contact 11 contactsthe column at the interface between the liquid metal and the slug ofnonconductive material, the circuit will be closed. An outstandingfeature of my new coulometric device is that it is completely reversiblesimply by reversing the polarity of potential applied between thecolumns. This is true whether the device is used as a simple operatingtime indicator or as a switch. Consequently, the device may also be usedas a circuit opening switch provided that its operation is started at atime when the anode column is in contact with the contact 11.

As previously stated, a part of the present invention is a novel methodfor the fabrication of coulometer devices such as that described in thepreceding portions of this specification as well as others. By usingthis method, coulometer devices may be fabricated simply andinexpensively as well as in extremely small sizes. As an illustration ofthe latter feature, a coulometer device according to the invention maybe made approximately the size shown in FIG. 1 of the drawing, but infact, I have, using my new method, manufactured many fully operativedevices of which the essential components occupy a volume which isapproximately A" X 1%" X A The method will be described with referenceto FIGS. 1, 2 and 3. A filamentary body such as a nickel-iron wire 12 isformed in the U-shape of the channel shown in FIG. 1 and is placed onthe surface of a base layer In. In this particular example of my newmethod the base layer is a sheet of transparent vinyl resin. A strip ofporous filter paper 6 is formed in a figure-8 shape as seen edge-on inthe exploded view of FIG. 2. Each of the loops of the strip of filterpaper so formed encloses one of the legs of the wire 12. Then anotherlayer 1!) of a thermoplastic vinyl resin is superposed on thecombination of the base layer, the wire 12 and the filter paper 6. Thisentire assembly is then subjected to heat and pressure as indicated bythe arrows for two purposes. The heat applied to the resin softens itand the pressure applied to the two layers causes the wire 12 and thefilter paper 6 to be pressed into the adjacent surfaces of the layers Inand 1b of thermoplastic material. The heat and pressure also serve tobond the base layer and the superposed layer of resin togehter with thewire and the filter paper encapsulated between the layers.

It should be noted here that the method is not restricted to the .use ofthermoplastic material for both layers. Either the base layer or thesuperposed layer may be thermoplastic and the other layer may be solelyfor the purpose of transmitting the pressure necessary to embed the Wireand the filter paper in the thermoplastic material. Furthermore, thenon-thermoplastic layer need not become a part of the final device forafter embedding the wire and paper in the thermoplastic layer, thenon-thermoplastic layer may be removed and a closure layer may be put inits place and bonded or adhered to the thermoplastic layer. Thepreferred method is, however, to use base and superposed layers, both ofwhich are thermoplastic material.

After the heat and pressure are removed, the wire is withdrawn endwisefrom between the layers of resin which are now bonded together as shownin FIG. 3, thus leaving within the laminated structure a channel whichis U-shaped in the plan view of FIG. 1 of substantially uniform crosssection. It should be noted at this point that portions of the legs ofthe channel also pass through the loops of the filter paper embedded inthe laminar structure.

Upon withdrawal of the wire from the channel electrolyte solution isinjected into the open channel by means of a hypodermic needle or othersuitable means. Because of the porous nature of the filter paper, theelectrolyte solution will be absorbed by it until the paper issaturated. The channel is then flushed with mercury so that it is fullof the liquid metal and there are no random air bubbles entrapped in thechannel. The mercury may also be injected into the channel by means of ahypodermic needle. The slug 7 of non-conductive material is thenintroduced into the channel through one of the open ends. If thenon-conductive material is to be a simple air bubble or a small quantityof liquid, it may be injected by means of a hypodermic needle and thenpushed along the channel by additional mercury until it is positioned atany desired location such as in the bow of the channel. There is thusformed in the channel two columns of mercury separated at theirinnermost ends by a slug of nonconductive material.

Electric contacts with the two columns of mercury in the channel areprovided as follows. A mercury-plated, nickel-iron wire is inserted intoeach of the open ends of the channel so that it is in contact with themercury column in that leg of the channel and these leads 8 and 9 arethen heat-sealed in place by inserting the marginal edge of thelaminated structure in a heated press to close the open ends of thechannel and securely embed portions of each of the wires in thethermoplastic material. I have found it useful to roughen the wires atthe places where they will be embedded in plastic so that they may noteasily be pulled out. The purpose of plating the wires before insertingthem in the channels is to insure good electric contact with the mercurycolumns.

The foregoing steps form the basic coulometer according to my invention.As will be apparent to those skilled in the tart, many modifications ofthe method will be made. For example, only one of the layers of thelaminated structure need be deformable under heat and pressure in whichcase the heat and pressure applied to the assembled structure willresult in the wire or other filamentary body being embedded only in thedeformable layer of the channel, while being bounded by thenon-deformable layer about a portion of its periphery, will beessentially entirely within the deformable layer. Any suitable porousmea) dium such as matted or compacted fibrous or cellular material maybe used to absorb the electrolyte and it will, according to its nature,be positioned in the laminate so that the electrolyte is in electricalcontact within the columns of liquid metal in the two legs of thechannel.

When one wishes to form the switch-type coulometric device having thecontact 11 located for example in the bow of the channel, the contactmay be formed by looping a small wire around the bow of the wire used toform the channel in the plastic material. At the time the U- shaped wireor other filamentary body is positioned on the base layer the steps ofthe method previously described are then followed through to the end andthe loop of contact wire which was formed around the channel formingwire will be securely and permanently positioned within the channelafter the channel forming wire is removed. Of course, the end of thecontact wire opposite the loop is made long enough to extend beyond theouter edge of the thermoplastic material so that it may be used as alead to connect the contact into an external circuit.

It should be apparent to those skilled in the art that my new method offorming a coulometer may also be adapted to form coulometers which donot incorporate the porous material extending between the two columns ofmercury in the channel. For example, my new method may be used to makeknown types of coulometric devices in which the electrolyte solutionoccupies a position in the channel between the innermost ends of the twocolumns of liquid metal.

I have illustrated in FIGS. 4 and 5 two means of applying thecoulometric devices according to my invention. In FIG. 4 I illustrate asimple circuit in which the coulometric device is used as an electricswitch. Here the device includes the contact wire 11 described inconnection with FIG. 1. The device is used to fire a flashbulb 14 at theend of some predetermined interval. The flashbulb is connected in serieswith a battery 15, a resistor 16, and the mercury columns in the legs 3and 4 of the channel. A storage capacitor 17 is connected in shunt tothe battery or other source of DC. potential. The contact wire 11 isconnected to the junction between one terminal of the flashbulb 14 andthe resistor 16.

In operation, the battery charges the capacitor 17 and it also serves asthe source of potential for the coulometric device. The coulometricdevice may be pre-set so that, at the specific current through theresistor, it will require some predetermined time for the anode columnto grow a ong the channel until it contacts the contact wire 11. In theterms I have previously used in the course of this specification and inthe claims, this is one means of detecting the interface between themercury column and the slug of non-conductive material.

It will be apparent that, so long as the slug of nonconductive materialis in the portion of the bow of the channel where the contact wire 11 islocated, the current through the fiashbulb will be limited by the valueof the resistor 16 which also determines the current flow through thecoulometric device. This current is selected so that it is not greatenough to cause the flashbulb to ignite.

When the anode column reaches the contact wire 11 the resistor 16 isshunted out of the circuit by the much lower resistance of the circuitincluding the contact wire 11, the anode column, the capacitor 17 andthe flashbulb 14. This permits the capacitor to discharge through thefiashbulb and the discharge current is suflicient to ignite theflashbulb.

In FIG. 5 I have illustrated a photoelectric means for detecting theinterface between the mercury column and the slug of non-conductivematerial. The coulometric device is connected in a conventional circuitincluding a battery 18 and a resistance 19. A light source such as thelight bulb 20 is positioned on one side side of the device and aphotoelectric cell 21 is positioned on the opposite side. A mask 22having a small aperture as indicated at 23 is positioned between thedevice and the photoelectric cell. The output of the photoelectric cellmay be connected to any suitable utilization device indicated generallyat 24. In this application the slug of non-conductive material betweenthe two columns of mercury in the channel of the device must betranslucent so that light from the bulb 20 will be transmitted throughit. The mercury itself is, of course, opaque and will interrupt thelight from the source. Thus, when the translucent non-conductivematerial in the channel is in the line between the source and theaperture of the mask, light will fall on the photoelectric cell, andwhen mercury is in the line between the source and the aperture of themask the light will be cut off from the photoelectric cell.

A particular feature of my new coulometric device is that the portionsof the mercury columns and the slug of non-conductive material in thebow of the channel are not in the circuit by which the device isenergized. This makes it practically possible to construct a devicewhich can function as a multiple olI-on-olT-on-off switch, for example,by introducing into the bow of the channel two or more slugs oftranslucent non-conductive material and separating these 'by slugs ofmercury 01' other opaque material which are free to move along thechannel. Thus, as the anode column of the device grows along the channelthe slugs of translucent and opaque materials are alternately pushedinto the line between the light bulb 20 and the aperture 23 in the mask22. As each interface between the adjacent slugs of translucent andopaque materials traverses this line, the response of the photoelectriccell is switched from off-to-on or onto-otf as the case may be.

In the foregoing description I have described in detail a particularembodiment of my invention and a particular method also in accordancewith my invention. It should be understood that the invention is notlimited to the details of either the device or the method as set forth.The invention is defined in the following claims.

I claim:

1. A method of forming a coulometric device, which method comprises thesteps of forming a filamentary body to a predetermined curvilinearconfiguration, positioning a body of porous material in spanningrelation between spaced positions along said filamentary body with saidporous body embracing at least a portion of the periphery of saidfilamentary body at each of said spaced locations, positioning saidfilamentary and porous bodies between superposed layers ofnon-conductive material which is deformable under pressure and whichwill retain a permanent set upon release of deforming pressure, applyingpressure to said superposed layers to cause said filamentary and porousbodies to be impressed into said layers and to cause said filamentarybody to form a channel in said layers and through said porous body,withdrawing said filamentary body from said channel, and injecting intosaid channel two columns of liquid metal such that their adjacent endsare spaced apart at a position intermediate the positions where thechannel penetrates said porous body.

2. A method according to claim 1 which further comprises the step ofimpregnating said porous body with an electrolyte material prior toinjecting into said channel said liquid metal, such that said porousbody is an electrolytic bridge joining said columns of liquid met-a1.

3. A method according to claim 1 wherein the step of injecting saidliquid metal into said channel includes spacing apart the adjacent endsof said columns by an electrically non-conductive material.

4. A method of forming a coulometric device comprising the steps:

(a) positioning a filamentary body in a predetermined configuration on asurface of a first layer of material,

(b) superposing on said filamentary body a second layer of materialwhich is deformable under pressure and will retain a permanent set uponrelease of said deforming pressure,

(c) applying pressure to said superposed layers to cause saidfilamentary body to be impressed into said deformable layer to form achannel therein,

(d) bonding said deformed layer to a base material such that saidchannel has openings only at its ends,

(e) withdrawing said filamentary body from the channel formed in saiddeformable layer, and

(f) inserting metal into said channel.

5. A method according to claim 4 wherein said deformed layer is bondedto said first layer.

6. A method according to claim 4 comprising the further step of applyingheat to said layers while said pressure is applied. 7 i

7. A method according to claim 4 comprising the further step of applyingheat during the bonding step.

References Cited by the Examiner UNITED STATES PATENTS 2,373,405 4/1945Lowit 29l56 JOHN F. CAMPBELL, Primary Examiner.

JOHN M. ROMANCHIK, JR., Assistant Examiner.

1. A METHOD OF FORMING A COULOMETRIC DEVICE, WHICH METHOD COMPRISES THESTEPS OF FORMING A FILAMENTARY BODY TO A PREDETERMINED CURVILINEARCONFIGURATION, POSITIONING A BODY A POROUS MATERIAL IN SPANNING RELATIONBETWEEN SPACED POSITIONS ALONG SAID FILAMENTARY BODY WITH SAID POROUSBODY EMBRACING AT LEAST A PORTION OF THE PERIPHERY OF SAID FILAMENTARYBODY AT EACH OF SAID SPACED LOCATIONS, POSITIONING SAID FILAMENTARY ANDPOROUS BODIES BETWEEN SUPERPOSED LAYERS OF NON-CONDUCTIVE MATERIAL WHICHIS DEFORMABLE UNDER PRESSURE AND WHICH WILL RETAIN A PERMANENT SET UPONRELEASE OF DEFORMING PRESSURE, APPLYING PRESSURE TO SAID SUPERPOSEDLAYERS TO CAUSE SAID FILAMENTARY AND POROUS BODIES TO BE IMPRESSED INTOSAID LAYERS TO CAUSE SAID FILAMENTARY BODY TO FORM A CHANNEL IN SAIDLAYERS AND THROUGH SAID POROUS BODY, WITHDRAWING SAID FILAMENTARY BODYFROM SAID CHANNEL, AND INJECTING INTO SAID CHANNEL TWO COLUMNS OF LIQUIDMETAL SUCH THAT THEIR ADJACENT ENDS ARE SPACED APART AT A POSITIONINTERMEDIATE THE POSITIONS WHERE THE CHANNEL PENETRATES SAID POROUSBODY.